Efficacy of Herbicide Options for Scotch Broom

Management

Tim MillerWSU Mount Vernon NWREC

Today’s Presentation

• Foliar treatments• Some thoughts on cut-stem/

thinline/basal bark treatments• Effects of soil residual herbicides on

Scotch broom seed germination

Foliar Herbicides• Triclopyr• Amine formulations (typified by Garlon 3A)• Choline formulation (Vastlan)• Ester formulations (typified by Garlon 4, or

a mixture with 2,4-D ester, Crossbow)• Rate

– 2 to 3 qt/a ester, 3 to 4 qt/a amine/choline (up to 2.25 gal/a is registered for Vastlan)

Foliar Herbicides• Aminopyralid• Milestone is straight aminopyralid,

Capstone is aminopyralid + triclopyr• Capstone is the preferred product,

although Milestone alone can be helpful in tank-mixture with other products

• Rate– 0.5 to 5% alone or in tank-mixture

Foliar Herbicides• Nonselective herbicides• Imazapyr (Habitat, Stalker, Chopper,

Arsenal, Polaris)– Rate 2 to 10%, mix with up to 20% crop

oil concentrate prior to application

• Glyphosate (lots and lots and lots of formulations)– Rate 1.5 to 2% Roundup Pro or equivalent

Foliar Herbicides• Two more selective herbicides• Both are tough on trees, so it’s hard to

recommend these for forested sites• Picloram (Tordon 22K and others)

– Weed Control in Natural Areas recommends 2 qt/a on noncropland, 1 qt/a on rangeland

• Aminocylcopyrachlor (Method, Perspective with chlorsulfuron (Telar), or Streamline with metsulfuron (Escort)– Rate 7.5 to 11.5 oz/a of Streamline

Other Possibilities to Consider for Control of Scotch Broom and Other Woody Species

–Hack and Squirt (Frill Cut)–Cut Stem (Cut Stump)–Basal Bark

Frill Cut or Hack and Squirt

The technique is to cut through rough bark into the sapwood, then to apply herbicide to the cambial area just beneath the bark (probably not very convenient for a small shrub like Scotch broom)

Basal Bark or Thin-Line Applications

No cutting is necessary if the bark is thin/smooth as in Scotch broom, as many herbicide/surfactant combinations can move through this type of bark and then throughout the plant

Cut-Stump or Cut-Stem Applications

The entire stem is cut through, and herbicide is applied to the freshly cut surface, especially to cambial tissuejust under the bark

Cut-Surface Applications with Dilute and Concentrated Solutions

• Rates vary by herbicide and technique!• Dilute solutions

– Mix 8 to 12 fluid ounces product with one gallon of water

• Use of the concentrated solution permits application to fewer cuts on the stem, especially for large diameter trees– Mix 2 quarts product with 1 quart water– Some products may be applied full-strength

How About The Seeds?• Glad you asked!• Recent data from Tim Harrington,

USDA Forest Service, Olympia

Duration of trial (days)0 15 30 45 60 75 90

See

dlin

g m

orta

lity

(%)

0

2

4

6

8

10

12

0

2

4

6

8

10

12

gravelly loamy sand

cobbly loamNon-treatedOust (3 oz/acre)Escort (1 oz/acre)Oust (1.5 oz/acre) + Escort (0.75 oz/acre)Oust (3 oz/acre) + Escort (1 oz/acre)

• Seedling mortality averaged 7% for treated soils versus 1% for non-treated soils.

Oust (sulfometuron) and Escort Can Persist in Moist Soil

90 days after application of Oust + Escort

Harrington, Weed Sci. 2009

Soil typecobbly loam gravelly loamy sand

See

dlin

g bi

omas

s (g

)

0.0

0.5

1.0

1.5

2.0Non-treatedOust (3 oz/acre)Escort (1 oz/acre)Oust+Escort (1.5+0.5 oz/acre) Oust+Escort (3+1 oz/acre)

Nontreated seedlings

Oust-treated seedlings

While not strongly active against Scotch broom, Oust at 90 days reduced seedling biomass, seedlings produced fewer lateral roots, and seedlings did not produce compound leaves

Harrington, Weed Sci. 2009

Preemergent Control of Scotch Broom with Auxinic Herbicides

Nontreated, Day 14

Aminopyralid, Day 14 Harrington, Weed Technology, 2014

In a growth chamber study, these herbicides caused over 80% seedling mortality